Sinks in bathrooms rapidly accumulate hair, bacteria, soap residue, and other unsanitary matter. Although it's straightforward to clean such accumulated material from the exposed portions of the sink, such as the bowl, the counter top, etc, it is very difficult to clean the recessed and concealed portions of a sink, such as the drain, and the overflow hole near the top of the bowl.
Further, because the surfaces of the drain, the overflow hole, and the conduit that connects the overflow hole to the sink drain are not seen, and are not easily accessible for cleaning, such hidden surfaces tend to accumulate substantial amounts of unsanitary biomaterial, such as dead skin, hair, bacterial, fungus, mold, and viruses.
Many people do not have an understanding of the inner structure of sinks to know about such hidden unsanitary surfaces, and even people with such understanding cannot clean such surfaces with currently available equipment. Consequently, they are often compelled to call a plumber when the drain gets excessively clogged. However, because they are often unaware of the odor and disease breeding ground within the inner contours of many sinks, they often fail to even attempt to clean and disinfect the inner and typically inaccessible surfaces inside many sinks.